The present invention relates to a system for electrically isolating a depending member on a field sprayer boom by providing a barrier for migration of charged particles toward a grounded potential portion of the field sprayer. In particular, the isolator is used in connection with a depending foam marker pipe at the outer ends of the boom for marking the path for travel of the sprayer.
Electrostatic field sprayers are known, and for example are shown in U.S. Pat. No. 4,788,617 to Davidson. Such electrostatic sprayers can be utilized for applying herbicides or pesticides, and aid in increasing sprayer efficiency.
Further, U.S. patent application Ser. No. 08/372,377, now U.S. Pat. No. 5,636,799 filed Jan. 13, 1995 owned by the same assignee as this application, illustrates a typical field sprayer using electrostatic principles for applying liquids. The present invention can be adapted for use on such a field sprayer.
In conduction electrostatic spraying, a very high potential liquid is sprayed from nozzles spaced along a boom, and the liquid spray drops are charged to in the range of 40,000 volts or more. The boom and the accessories are maintained at substantially ground potential, so the liquid particles are attracted to the lower voltage components. The accumulated droplets form paths for shorting out the high voltage charge.
Atmospheric conditions may also cause condensation of water or the formation of dew on the sprayer boom and other components, particularly during use in the early morning or evening. This moisture may also cause shorting out of the high voltage system.
Various types of shields have been advanced for preventing migration of electrostatically sprayed liquids to a grounded component. The problems persist particularly where a folding boom is utilized, as is the case with the large field sprayers. Inverted cup isolators that have been advanced serve as isolators in working position, but when they are on an outer end of the boom and the boom is folded back on itself, the cups open upwardly and collect water, which then serves to provide a wet path for voltage leakage as soon as the boom is returned to its usable extended position.
The foam used for foam markers is at substantially ground potential. The insulating pipes that carry the foam are connected to grounded components, so it is important to prevent any conductive paths from being formed on the pipe. The foam is generally dropped adjacent to the outer spray nozzles, so it tends to become wetted with electrostatically charged particles and these tend to migrate back to the supports for the depending pipes carrying the foam.
The one mode of failure is that the current may penetrate the material of the foam tubes and reach the foam (which is a conductor) and then reach the foam source via the foam in the remainder of the tube. This is prevented by the dielectric properties of the material used for the tube. Current may also travel along the foam tube (after it has been wetted by the above mentioned reasons) and reach the foam outlet. As soon as the current reaches the foam outlet, it will be conducted back to "ground" because of the conductive nature of the water based foam. This is prevented by the isolator discs of the present invention.